That's not why it's done though. It will often be accompanied by pseudoscience justification that doesn't hold up to rationality or accepted science.

Even if that wasn't the case though, what do you expect to be gained by enforcing that discipline?

You have a finite amount of variables you can control, and wasting time thinking about details that don't matter is a massive drain. When training for a show, you should be focussing your effort on the things that make the biggest difference: overall food intake, macros, exercise, resistance training, meal timing, micros, etc.